This invention relates generally to a cover for hatches, manholes and the like, and more particularly to a hatch cover with a spring assembly to assist in lifting the hatch cover lid. A method of assembling the spring assembly is also disclosed.
Today, sewers, subway systems, electrical wiring, plumbing, and a host of other modern necessities are located underground. These necessities require the capability of being accessed. As such, openings large enough to accommodate individuals, equipment, pallets of material or the like are commonplace. These openings generally take the form of manholes or hatches.
Many manholes or hatches must be covered because they are needed in places where they are crossed over by pedestrians, cars, trucks, and even aircraft. The covers on the manholes or hatches must be heavy enough so that the air or water pressure inside the cavity beneath them will not lift the cover off the opening. More important, covers need to have sufficient structural integrity so that they will not be compromised under the weight of vehicles passing over them.
Covers for openings along streets, roadways, runways, and the like are constructed of iron, steel, aluminum, concrete, plastic or other strong materials. Such covers may weigh several hundred pounds depending on the size of the opening needed to access the cavity. Periodically, covers are lifted so that the cavity can be accessed. Due to the weight of the covers, service personnel must normally work in pairs or use additional equipment to ensure safe handling of the covers.
Attempts have been made to solve the problem of safely and easily opening and closing the covers of the underground openings. These attempts involve using covers with spring-biased assemblies to assist in the lifting of the covers. For example, in U.S. Pat. No. 5,788,406, issued to Hernandez on Aug. 4, 1998 shows a device to assist in the opening of a manhole cover. In Hernandez, a spring and pivot rods are attached to both a cover and a stepped skirt that is seated into the opening. The cover may be lifted so that a worker may access the opening. However, the diameter of the stepped skirt is much larger than the actual opening diameter, and the biasing mechanism appears somewhat complex. Both characteristics add to the expense of the entire cover.
A simpler prior art device is shown in FIG. 1. The biasing assembly “B” is connected to the wall “W” defining the opening, and to the cover “C.” Walls are commonly constructed from concrete, see partial wall “W” shown by way of example. These hinged covers have a spring “S” mounted to the wall of the structure and/or frame. However, there are several disadvantages with this particular design. First, the biasing assembly B encroaches into the opening, which requires workers to negotiate the assembly when entering or exiting the openings. Such negotiation is made more difficult if the opening is small and the worker is carrying tools and equipment. Second, this post construction modification can place a stress concentration at or near the attachment site. Over time, material fatigue may cause failure of the spring mounting assembly and/or failure of the fasteners used to connect it to the wall. In addition, the pressure from the spring can cause the frame to break free form the surrounding concrete.
Other prior art spring assemblies are often post construction modifications for existing hatches or manholes. However, it is more complicated to retrofit a spring assembly onto an existing hatch or manhole that one that is already in existence. Further, spring-biased assemblies such as that shown in FIG. 1 can be difficult to service because the spring is connected to the wall W and cannot be practically removed from the opening without damage.
Accordingly, a need exists for a spring assembly for lifting lids of hatch or manhole covers, such assembly containing a minimal number of parts to reduce complexity and/or costs associated with manufacturing and servicing of the assembly. Further, a need exists for a spring assembly that does not significantly impede workers, equipment and other items from entering and exiting the opening.